Full list of all 72 Fallout 3 achievements worth 1,550 gamerscore. It takes around 60-80 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 22 achievements worth 550 Gamerscore.
Got the Pip-Boy 3000
Took the G.O.A.T.
Completed "Escape!"
Completed "Following in His Footsteps"
Completed "Galaxy News Radio"
Completed "Scientific Pursuits"
Completed "Tranquility Lane"
Completed "The Waters of Life"
Completed "The Superhuman Gambit"
Completed "Head of State"
Completed "The Replicated Man"
Completed "Blood Ties"
Completed "The Power of the Atom"
Completed "Tenpenny Tower"
Completed "Stealing Independence"
Completed "Trouble on the Homefront"
Reached Level 8 with Bad Karma
Killed 300 creatures
Placed a grenade or mine while pickpocketing
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Finding the Garden of Eden"
Completed "The American Dream"
Completed "Take it Back!"
Completed "Big Trouble in Big Town"
Completed "The Wasteland Survival Guide"
Completed "Those!"
Completed "Oasis"
Completed "Strictly Business"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Reilly's Rangers"
Reached Level 8 with Good Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Good Karma
Killed 300 people
Picked 50 locks
Discovered 100 locations
Completed "The Nuka-Cola Challenge"
Completed "Agatha's Song"
Reached Level 8 with Neutral Karma
Reached Level 14 with Neutral Karma
Reached Level 20 with Neutral Karma
Made one of every custom weapon
Won 50 Speech Challenges
Hacked 50 terminals
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Collected 20 Vault-Tec Bobbleheads
Completed "Aiding the Outcasts"
Completed "The Guns of Anchorage"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "Into The Pitt"
Completed "Unsafe Working Conditions"
Completed "Free Labor"
Found All 100 Steel Ingots
Completed "Death From Above"
Completed "Shock Value"
Completed "Who Dares Wins"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "The Local Flavor"
Completed "Walking With Spirits"
Completed "A Meeting of the Minds"
Discovered all locations within Point Lookout
Completed "Not of This World"
Completed "Among the Stars"
Completed "This Galaxy Ain't Big Enough…"
Collected all Alien Captive Recordings